Labour are investigating claims of “political blackmail” after a senior party official was accused of pressuring a prospective candidate to stand down in favour of a pro-union rival.

The unnamed aide threatened to withdraw lucrative contracts from Blue State Digital unless Gregor Poynton, the communications company’s political director, withdrew from the race to become Labour’s candidate in Falkirk, according to media reports.

Another Labour supporter allegedly ordered party officials to approve last-minute block membership applications in order to help Kate Murphy, who was backed by the Unite union.